Re: [PATCH V3 1/3] mm/memory_hotplug: Prevalidate the address range being added with platform

From: David Hildenbrand
Date: Wed Jan 20 2021 - 07:03:40 EST

On 20.01.21 09:33, Anshuman Khandual wrote:
> On 1/19/21 5:51 PM, David Hildenbrand wrote:
>> On 18.01.21 14:12, Anshuman Khandual wrote:
>>> This introduces memhp_range_allowed() which can be called in various memory
>>> hotplug paths to prevalidate the address range which is being added, with
>>> the platform. Then memhp_range_allowed() calls memhp_get_pluggable_range()
>>> which provides applicable address range depending on whether linear mapping
>>> is required or not. For ranges that require linear mapping, it calls a new
>>> arch callback arch_get_mappable_range() which the platform can override. So
>>> the new callback, in turn provides the platform an opportunity to configure
>>> acceptable memory hotplug address ranges in case there are constraints.
>>> This mechanism will help prevent platform specific errors deep down during
>>> hotplug calls. This drops now redundant check_hotplug_memory_addressable()
>>> check in __add_pages() but instead adds a VM_BUG_ON() check which would
>> In this patch, you keep the __add_pages() checks. But as discussed, we
>> could perform it in mm/memremap.c:pagemap_range() insted and convert it
>> to a VM_BUG_ON().
> Just to be sure, will the following change achieve what you are
> suggesting here. pagemap_range() after this change, will again
> be the same like the V1 series.

Yeah, as we used to have in v1. Maybe other reviewers (@Oscar?) have a
different opinion.

If you decide to leave as-is, please fixup the patch description. Thanks!


David / dhildenb